1. Field of the Invention
The present invention relates to an electron emission device, and in particular, to an electron emission device which involves improved structure of electron emission regions and driving electrodes to enhance the emission efficiency, and a method of manufacturing the electron emission device.
2. Description of Related Art
Generally, electron emission devices are classified into those using hot cathodes as an electron emission source, and those using cold cathodes as the electron emission source. There are several types of cold cathode electron emission devices, including a field emitter array (FEA) type, a metal-insulator-metal (MIM) type, a metal-insulator-semiconductor (MIS) type, and a surface conduction emitter (SCE) type.
The MIM type and the MIS type electron emission devices have a metal/insulator/metal (MIM) electron emission region and a metal/insulator/semiconductor (MIS) electron emission region, respectively. When voltages are applied to the metallic layers or to the metallic and the semiconductor layers, electrons are migrated and accelerated from the metallic layer or the semiconductor layer having a high electric potential to the metallic layer having a low electric potential, thereby making the electron emission.
The SCE type electron emission device includes first and second electrodes arranged on a substrate parallel to each other, and a conductive thin film disposed between the first and the second electrodes. Micro-cracks are made at the conductive thin film to form electron emission regions. When voltages are applied to the electrodes while making an electric current flow to the surface of the conductive thin film, electrons are emitted from the electron emission regions.
The FEA type electron emission device is based on the principle that when a material having a low work function or a high aspect ratio is used as an electron emission source, electrons are easily emitted from the material due to the electric field under the vacuum atmosphere. A sharp-pointed tip structure based on molybdenum Mo or silicon Si, or a carbonaceous material, such as carbon nanotube has been developed to be used as the electron emission region.
The electron emission device using the cold cathode basically has first and second substrates forming a vacuum vessel, and electron emission regions formed on the first substrate together with driving electrodes for controlling the electron emission of the electron emission regions. Phosphor layers are formed on the second substrate together with an anode electrode for accelerating the electrons emitted from the first substrate toward the phosphor layers, thereby displaying the desired images.
The FEA type electron emission device has cathode and gate electrodes as the driving electrodes. The cathode and the gate electrodes are placed on different planes with an insulating layer therebetween. Any one of the cathode and the gate electrodes receives a scan driving voltage, and the other electrode receives a data driving voltage such that electrons are emitted from the electron emission regions connected to the cathode electrode.
It is necessary with the FEA type electron emission device that the emission efficiency should be enhanced to realize a high luminance display screen. The emission efficiency is determined depending upon various factors, such as a contact resistance between the cathode electrode and the electron emission region, the dimension of the effective electron emission portion of the electron emission region, and the distance between the electron emission region and the gate electrode.
In case the contact resistance between the cathode electrode and the electron emission region is high, it becomes difficult to apply the required electric current to the electron emission regions, so the emission efficiency is deteriorated. The effective electron emission portion is the portion of the electron emission region where the electron emission is intensive. The emission efficiency increases as the effective electron emission increases. Furthermore, the strength of the electric field formed around the electron emission regions increases as the distance between the electron emission region and the gate electrode decreases, thereby enhancing the emission efficiency.
However, with the above-described electron emission device, the above factors are not all optimized, and hence, enhancement of the emission efficiency is limited so that a high luminance display screen cannot be obtained. Of course, it is possible to solve such a problem by heightening the driving voltage. However, in such a case, power consumption is increased, and high cost drivers should be used, resulting in increased production cost of the electron emission device.